In recent years, with improvement of a semiconductor technology and development of a new algorithm, power line communication (PLC) using a band of 20 MHz to 30 MHz and having a communication speed of 200 Mbps at maximum has been put to practical use (retrieve, e.g., High-Speed Power Line Communication System Overview authored by High-Speed Power Line Communication Promoter Alliance of Japan, homepage URL “http://www.plc-j.org/about_plc_system.htm”, Dec. 16, 2004).
The power line communication attracts attention as the third broadband technology following ADSL using a cable and a telephone line. Especially, in Japan, the power line communication also attracts great attention as a solving method of the last mile problem in a Fiber To The Home (FTTH) service. That is, for example, when a PLC device is installed at a utility pole to perform the power line communication by use of an already laid power line, an enormous expense for newly laying an optical fiber cable from the utility pole to a house can be saved.
The PLC is a medium sharing technology. Therefore, when the PLC device is installed at a transformer of the utility pole, the communication can be performed with all power sockets to which power is supplied from the transformer. For example, in Japan, the utility pole is already provided with the optical fiber cable in many cases, and one transformer supplies power to ten to twenty houses in many cases, so the PLC will rapidly prevail. In the PLC, the communication can be performed using the power socket already disposed in the house of general household, and therefore, it is supposed that the PLC is broadly used by general users.